Semiconductor light emitting devices are used either as an ultraviolet-, blue- or green light emitting diode element, or as an ultraviolet-, blue- or green laser diode element. In particular, group III-V nitride semiconductor light emitting devices having a light emitting layer composed of a group III-V nitride semiconductor that uses nitrogen as a group V element are widely used.
A semiconductor light emitting device substrate for supporting this light emitting structure is formed of sapphire, silicon carbide, silicon or the like, and usually has a lower refractive index than that of a semiconductor layer or the like that constitutes the light emitting structure.
A group III-V nitride semiconductor light emitting device has a basic structure in which an n-type semiconductor layer, a light emitting layer and a p-type semiconductor layer are laminated sequentially on a substrate made of sapphire or the like, and an n-type electrode and a p-type electrode are formed on the n-type semiconductor layer and on the p-type semiconductor layer, respectively. Then, light emitted in the light emitting layer is extracted from the p-type electrode side and/or the substrate side.
A portion of light generated by the light emitting structure is totally reflected repeatedly between the semiconductor light emitting device substrate and the light emitting structure in accordance with the difference in the refractive indices between the semiconductor light emitting device substrate and the light emitting structure. As a result, the light generated by the light emitting structure is attenuated inside the light emitting structure.
In order to solve this problem, by laminating the semiconductor layer after forming an uneven structure on the substrate in advance, various methods have been proposed for changing the light angle to suppress the total reflection by using the uneven structure of the aforementioned uneven substrate, thereby improving the light extraction efficiency (see Patent Documents 1 to 3 and Non-Patent Document 1).
For example, in Patent Documents 1 and 2, it has been proposed to form a mask pattern on a substrate using a photolithography method, form an uneven structure on the substrate by dry etching the aforementioned substrate using the mask pattern, and then form a semiconductor layer on the uneven structure.
In addition, in Patent Document 3, it has been proposed to form an uneven structure on a substrate by dry etching the aforementioned substrate using inorganic particles arranged on the substrate as an etching mask, and then form a semiconductor layer on the uneven structure. In Patent Document 3, as a preferred method of arranging inorganic particles on a substrate, a method has been proposed in which, using a slurry prepared by dispersing inorganic particles in a medium such as water, the aforementioned substrate is immersed in the aforementioned slurry, or the aforementioned slurry is applied or sprayed on the aforementioned substrate followed by drying. In addition, in order to form a favorable semiconductor layer, it has been accepted that inorganic particles should be arranged on the substrate with a coverage of 90% or less.
Further, in Non-Patent Document 1, studies have been made on the relationship between the pitch of an uneven structure to be formed on a substrate and the effect of improving light extraction efficiency. In addition, it has been described that the effect of improving the light extraction efficiency was hardly achieved by an uneven structure with a pitch of 1,000 nm, whereas 170% of light extraction efficiency was achieved by an uneven structure with a pitch of 500 nm, as compared to the case of using a flat substrate.
It should be noted that as a method of producing a fine structure having an uneven structure with a pitch of 1 μm or less, an electron beam lithography method, an interference exposure method and the like have been known conventionally.